Initially, gas generators used to inflate large emergency exit ramps or slides on commercial aircraft used a pyrotechnic gas generant that produced a large volume of hot gas on combustion. However, it was soon discovered that the temperature of the hot gas was sufficiently high to burn the fabric used to construct the exit ramp or slide, as well as anyone using the ramp or slide. In addition, because the temperature of the inflation gas was well above the ambient temperature, the ramp or slide would partially deflate as the gas cooled and the pressure of the gas decreased as a result of the temperature change. This was particularly true if the airplane was required to put down in cold water, such as that found in northern oceans.
In an attempt to overcome the deficiencies of pyrotechnic inflators, as described above, such rafts and ramps or slides were inflated using a compressed gas, as disclosed in U.S. Pat. No. 4,355,987 to Miller and U.S. Pat. No. 5,586,615 to Hammer et al. However, where only a compressed gas is utilized to inflate the raft or ramp or slide, a large drop in temperature occurs in the gas as it expands, often causing ice to form, which can block the flow of gas. To overcome these problems, emergency exit ramps or slides and rafts presently carried on commercial aircraft typically employ an inflation system comprising a compressed gas source and an aspirator, such as that disclosed in U.S. Pat. No. 4,368,009 to Heimovics et al. As the compressed gas is released, the vacuum produced thereby causes the aspirator to ingest about four times as much gas as is supplied by the compressed gas source.
However, even these aspirator systems have several disadvantages. They are large and heavy, and produce gas at a relatively slow rate. Moreover, the rate is further slowed as the back pressure of the gas in the object being inflated increases. This can cause difficulties, e.g., in the deployment of an emergency ramp or slide from an aircraft that has landed in water. Because of the slow rate of inflation, a ramp or slide may float under the aircraft before becoming fully inflated, and become trapped. Even where the ramp or slide does not become trapped, the slow rate of inflation may force occupants of the aircraft to wait for the ramp or slide to fully inflate, which can result in panic on the part of the passengers. Therefore, it is desirable to minimize the amount of time required to inflate the ramp or slide.
The weight of an aspiration inflator system is high even when the high pressure container required to store the pressurized gas is made from lightweight materials, such as titanium with a wound graphite filament overwrap. This reduces the carrying capacity of the aircraft. These systems also present a maintenance problem to ensure that the required gas pressure is maintained, and that the aspirator will function properly. Moreover, even using a high pressure gas source, an aspiration system can only provide a maximum pressure of about 2 psig, i.e., about 2 psi above normal atmospheric pressure. Therefore, to support occupants from the aircraft, an inflatable member inflated with an aspirator system must be much larger than would be required if the member was inflated to a higher pressure.
Therefore, there remains a need for a rapid, relatively low weight inflator that is able to inflate an aircraft emergency exit ramp or slide, life raft, or other relatively large inflatable objects rapidly and to a relatively high pressure. The present invention provides such an inflator.